Addition fluoroalkanes

In particular, commercial periluoroalkanes and -cycloalkanes (e.g., Fluorinert-, Flutec-, Fom-blin-, Galden-, Hostinert-type products) have great chemical, biochemical and thermal stability. They are rated, biochemically, as comparably harmless or practically nontoxic, which arc the lowest toxicity ratings.15-25-173 Additional fluoroalkanes are listed in the literature, see, for example, refs 6 and 191. 

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

The mixtures bromine trifluoride/bromine and iodine pentafluoride/iodine can be successfully employed to prepare bromo- and iodo-substituted fluoroalkanes by addition to poly-fluoroalkenes. The reactions are carried out, in the presence of catalysts aluminum, aluminum/ aluminum triiodide9 or without a catalyst,10 in steel reactors at room temperature or with heating. In most cases the addition products are obtained in high yield (see Table 1). 

The addition of bromine monofluoride to alkenes using equimolar quantities of /V-bro-moamides in excess anhydrous hydrogen fluoride gives the expected l-bromo-2-fluoroalkanes and small amounts (3-8 %) of isomeric 2-bromo-l-fluoroalkanes.29 1-Bromo-2-fluoroheptane can be prepared in 60-77% yield from hept-l-cnc, /V-bromoacetamide and hydrogen fluoride in diethyl ether at — 78"C.30 The bromofluorination of methyl methacrylate (1) with 1,3-di-bromo-5.5-dimethylhydantoin (DBH) and liquid hydrogen fluoride exemplifies this procedure.31... 

Tertiary polyfluoro alcohols, l,l,l,3,3,3-hexafluoro-2-methylpropan-2-ol, 1,1,1,3,3-penta-fluoro-2-methylpropan-2-ol and l,l,3,3-tetrafluoro-2-methylpropan-2-ol, on treatment with sulfur tetrafluoride undergo dehydration to give the respective alkenes 7, but not fluoroalkanes small amounts of byproducts resulting from the addition of hydrogen fluoride to the C = C bond of the resultant alkcncs are also formed.54... 

The type of products formed in reactions of /(-hydroxy acids with sulfur tetrafluoride depends on the substituents on the carbon alom adjacent to the hydroxy group. Acids such as 3-hy-droxypropanoic acid (21) and 3-hydroxybutanoic acid (22) give, in addition to 1,1,1,3-tetra-fluoroalkanes, mainly dimeric products, i.e. fluorinated esters or ethers, together with small amounts of unsaturated acid fluorides. In contrast, n7C -4,4,4-trifluoro-3-hydroxybutanoic acid (23), depending on the reaction conditions, affords 3,3,3-trifluoro-l-(lrifluoromethyl)propyl fluorosulfite or a mixture of 1,1,1.2,4,4,4-hcptafluorobutanc and l,l,1.4.4,4-hcxafluorobut-2-ene.116... 

Complexes with a five-membered fluoroalkane ring are assumed to form through an intermediate state with two molecules of CF2=CF2 coordinated to the metal (22b). The addition of the second alkene molecule to the complex (22a) may be prevented by the coordination of the tridentate ligand p3 in the place of two PPh3 groups. In this case the... 

Each additional aliphatic alcohol function (-OH) above one Each additional aromatic nitrogen within a single ring above one A fluoroalkane with only one function A chloroalkane with only one chlorine A totally chlorinated chloroalkane A totally fluorinated fluoroalkane A totally halogenated halofluoroalkane... 

Early attempts to add chlorine fluoride to alkenes led only to chlorine addition however, control of temperature and the correct choice of solvent allow addition of a positive chlorine to give a chloronium ion followed by fluoride ion attack, so that overall CIF addition takes place giving a-chloro-jS-fluoroalkanes. 

Because of the extraordinary strength of the carbon-fluorine bond, transition metal-mediated activation of fluoroalkanes and arenes is not easy to achieve. Nevertheless, activation of the C-F bond in highly electron-deficient compounds such as 2,4,6-trifluoropyrimidine, pentafluoropyridine, or hexafluorobenzene is possible with stoichiometric amounts of bis(triethylphosphano) nickel(O) [101] (Scheme 2.45). More recently Herrmann and coworkers [102] have described a variant of the Kumada-Corriu cross-coupling reaction [103] between fluorobenzene and aryl Grignard compounds which uses catalytic amounts of nickel carbene complexes. Hammett analysis of the relative kinetic rate constants indicated that the reaction proceeds via initial oxidative addition of the fluoroaromatic reactant to the nickel(O) species. 

Oxidative addition of C-F bonds to low-valent metal complexes constitute one of the routes in activation of fluoroalkanes and fluoroarenes [71, 72], The chemical activation of carbon-fluorine bonds has attracted much attention since functionalization of C-F compounds gives various fluoroorganic derivatives, which have many technological applications. Typical examples of oxidative addition of C-F bonds [73] are shown in Scheme IV.36. 

We classify the fundamental processes of intermolecular G-F bond activation in the following six categories (i) oxidative addition of fluorocarbon, (ii) M-G bond formation with HF elimination, (iii) M-G bond formation with fluorosilane elimination, (iv) hydrodefluorination of fluorocarbon with M-F bond formation, (v) nucleophilic attack on fluorocarbon, and (vi) defluorination of fluorocarbon (Scheme 4). Table 2 shows the occurrence of these processes for intermolecular G-F activation, classified according to the type of G-F bond. For instance, oxidative addition is a characteristic process for fluoroaromatics but not for fluoroalkanes, while defluorination is characteristic of fluoroalkanes but not fluoroaromatics. We include processes as intermolecular even if they involve coordination of the fluorocarbon in one of the modes in Section 1.26.1.1 prior to G-F bond breaking. Notice that processes (ii), (iii), and (iv) could be described as cr-bond metatheses we have avoided this descriptor, since it has mechanistic connotations that are only appropriate in some cases. It should also be recognized that secondary processes may make some reactions awkward to classify under this scheme. 

Addition of HF to alkenes has been shown to follow Markovnikov s rule (Sharts, C. M. Sheppard, W. A. Org. React. 1974,21,125 and references therein). Direct addition of HF is seldom carried out because of the danger of working with that reagent and because of the development of newer synthetic reagents. Moreover, it is both safer and more convenient to use KF to synthesize a 2-fluoroalkane from the corresponding 2-chloroalkane than to add HF to a 1-alkene. 

Ligand substitutions of bound fluoroalkanes and noble gases have also been studied. In perfluorocyclohexane, the reaction of Cr(CO)5 (CgFj2) with CO yields Cr(CO)j with a rate constant that is 10 times larger than that for recombination in cyclohexane. Similar fast kinetic studies have been conducted on 16-electron complexes bound by noble gases. The reactions of Cp Rh(CO)(Kr) with alkanes forms Cp rih(CO)(alkane) prior to oxidative addition of the alkane. Kinetic studies on these processes have suggested that the... 

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